Water out alarm determination

ABSTRACT

The present disclosure provides for an improved method of determining a water out condition in a humidified gases supply apparatus. The method includes a two-step process including a primary determination of a water out condition and a secondary determination of a water out condition. This primary determination is made during observation of the normal operation of the apparatus. During the secondary determination the method takes temporary control over the humidifying part of the apparatus. The secondary determination confirms or contradicts the primary determination.

INCORPORATION BY REFERENCE TO PRIORITY APPLICATION

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

FIELD OF THE DISCLOSURE

The present disclosure relates to humidification systems for gases to besupplied to a patient.

BACKGROUND

For a range of applications, it is beneficial to humidify gases beingsupplied to a patient. These applications include where the gases arefor breathing by the patient and where the gas is being supplied duringsurgery to the patient. In the case of breathing gases, the humidityincreases patient comfort and the humidified gases are less prone todrying out the tissues of the patient airway. In the case of surgicalgases, the humidified gases reduce the drying out of exposed tissue andimprove post-operative outcomes.

SUMMARY

In a gases humidification system incorporating a humidification chamberfor humidifying gases for supply to the patient, it is important that acertain minimum level of water is maintained in order for the humidifierto have the ability to supply water vapor to the gases flow.Accordingly, it is important for a healthcare professional administeringthe humidified gases to a patient, or the patient themselves in the caseof home-based administration, to check the water level and add morewater when required. This task is often overlooked resulting in a breakin operation of the humidification of the airflow or, in some cases,damage to the respiratory assistance device.

Although water out alarms have been incorporated into respiratoryhumidification devices, the alarms are often susceptible to false alarmsin situations where the chamber is not actually empty. False alarmsoften cause significant concern to non-healthcare professionals who areunsure if the device is working properly. False alarms, when they occuroften, also cause healthcare professionals to ignore true alarms whenthey do occur.

The present disclosure provides a system for optimizing alarm criteriaselection to minimize the risk of a false alarm. The present disclosureprovides multiple different methods for determining a water outcondition and a selection criteria based on operating conditions forselecting an advantageous water out determination method.

It is an object of the present disclosure to provide a breathingassistance apparatus which goes some way to overcoming theabovementioned disadvantages or which at least provides the public orhealthcare professionals with a useful choice.

Accordingly in a first aspect, the disclosure may broadly be said tocomprise a respiratory assistance system for humidifying a flow of gasescomprising: a humidification chamber comprising an inlet and an outletto allow gases to pass through the humidification chamber, thehumidification chamber adapted to hold a quantity of water, a heateradjacent the humidification chamber, the heater adapted to provide heatto the quantity of water in the humidification chamber, a flow sensorpositioned on the humidification chamber, a temperature sensorassociated with the humidification chamber, and a controller inelectronic communication with heater plate, the flow sensor and thetemperature sensor, wherein the controller is configured to determine atleast one operational state based on a therapy mode and a flow rate andto select at least one water out detection method based on thedetermined operational state. The operational state is dependent on theflow rate in relation to a flow rate threshold.

The water out detection methods can include a passive water outdetection method, an active water out detection method, and a passivewater out detection method in conjunction with an active water outdetection method.

The respiratory assistance system can also include a user interfaceconfigured to permit a person to select the therapy mode from apredetermined list of therapy modes. The predetermined list incorporatesan invasive mode, a non-invasive mode, and a high flow, unsealed therapymode.

To those skilled in the art to which the disclosure relates, manychanges in construction and widely differing embodiments andapplications of the disclosure will suggest themselves without departingfrom the scope of the disclosure as defined in the appended claims. Thedisclosures and the descriptions herein are purely illustrative and arenot intended to be in any sense limiting.

The term “comprising” is used in the specification and claims, means“consisting at least in part of”. When interpreting a statement in thisspecification and claims that includes “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present disclosure will be described withreference to the accompanying drawings.

FIG. 1 a is a flow diagram illustrating the overall process fordetermining an absence of water in a humidifier chamber in accordancewith the present disclosure.

FIG. 1 b is a flow diagram illustrating another embodiment of theoverall process for determining an absence of water in a humidifierchamber in accordance with the present disclosure.

FIG. 2 is a flow diagram illustrating the overall process fordetermining an absence of water in a humidifier chamber in accordancewith an alternative embodiment of the present disclosure.

FIG. 3 is a flow diagram illustrating an active water out detectionmethod for determining an absence of water in a humidifier chamber inaccordance with the present disclosure.

FIG. 4 a shows a schematic view of a user receiving humidified air, withthe user wearing a nasal mask and receiving air from a modularblower/humidifier breathing assistance system.

FIG. 4 b shows a schematic view of a user receiving humidified air,where the user is wearing a nasal cannula and receiving air from amodular blower/humidifier breathing assistance system.

FIG. 5 shows a schematic view of a user receiving humidified air, wherethe user is wearing a nasal mask and receiving air from an integratedblower/humidifier breathing assistance system.

FIG. 6 shows a schematic view of a user receiving humidified air, wherethe user is wearing a nasal cannula, the breathing assistance systemreceiving gases from a central source via a wall inlet and providingthese to a control unit, which provides the gases to a humidifierchamber in line with and downstream of the control unit.

FIG. 7 is a plot against time of a function of heater plate power,heater plate temperature, filtered water level, and chamber outlettemperature, according to an experiment conducted to test a water outdetection method using the present disclosure.

DETAILED DESCRIPTION

The present description provides a respiratory assistance systemconfigured to supply multiple therapy modes and determine whether thewater level within a humidification chamber has reached below anacceptable threshold level. The system selects an appropriate water outdetection method based on the operational state of the system, which inturn relates to the particular therapy mode selected by a user and agases flow rate. The system therapy modes can include an invasive,non-invasive, and a high flow, unsealed mode or any other modes known tothose of skill in the art. The high flow, unsealed therapy mode (hereinreferred to as Optiflow® mode) is marketed as Optiflow® by Fisher andPaykel Healthcare Limited of Auckland, New Zealand.

A schematic view of a user 2 receiving air from a respiratory assistancebreathing unit and humidifier system 1 according to a first examplesystem configuration is shown in FIGS. 4 a and 4 b . The system 1provides a pressurized stream of heated, humidified gases to the user 2for therapeutic purposes, including, for example, to reduce theincidence of obstructive sleep apnea, to provide CPAP therapy, toprovide humidification for therapeutic purposes, or similar. The system1 is described in detail below.

The assisted breathing unit or blower unit 3 has an internal compressorunit, flow generator or fan unit 13—generally this could be referred toas a flow control mechanism. Air from atmosphere enters the housing ofthe blower unit 3 via an atmospheric inlet 40, and is drawn through thefan unit 13. The output of the fan unit 13 is adjustable—the fan speedis variable. The pressurized gases stream exits the fan unit 13 and theblower unit 3 and travels via a connection conduit 4 to a humidifierchamber 5, entering the humidifier chamber 5 via an entry port or inletport 23.

In alternative embodiments, the assisted breathing unit may comprise aventilator. The ventilator may have fans or turbines configured togenerate air flow. In some embodiments, the ventilators may receivegases from a compressed air source, such as a tank. The ventilators maythen use valves to control the delivery of air to the humidificationchamber 5.

The humidifier chamber 5 in use contains a volume of water 20. In someembodiments, in use the humidifier chamber 5 is located on top of ahumidifier base unit 21 which has a heater plate 12. The heater plate 12is powered to heat the base of the chamber 5 and thus heat the contentsof the chamber 5. As the water in the chamber 5 is heated it evaporates,and the gases within the humidifier chamber 5 (above the surface of thewater 20) become heated and humidified. The gases stream entering thehumidifier chamber 5 via inlet port 23 passes over the heated water (orthrough these heated, humidified gases—applicable for large chamber andflow rates) and becomes heated and humidified as it does so. The gasesstream then exits the humidifier chamber 5 via an exit port or outletport 9 and enters a delivery conduit 6.

When a ‘humidifier unit’ is referred to in this specification withreference to the disclosure, this should be taken to mean at least thechamber 5, and if appropriate, the base unit 21 and heater plate 12.

The heated, humidified gases pass along the length of the deliveryconduit 6 and are provided to the patient or user 2 via a user interface7. The conduit 6 may be heated via a heater wire (not shown) or similarto help prevent rain-out.

The user interface 7 shown in FIG. 4 a is a nasal mask which surroundsand covers the nose of the user 2. However, it should be noted that anasal cannula (as shown in FIG. 4 b ), full face mask, tracheostomyfitting, or any other suitable user interface could be substituted forthe nasal mask shown. A central controller or control system 8 islocated in either the blower casing (controller 8 a) or the humidifierbase unit (controller 8 b). In modular systems of this type, a separateblower controller 8 a and humidifier controller 8 b may be used, and thecontrollers 8 a, 8 b may be connected (e.g. by cables or similar) sothey can communicate with one another in use. In some embodiments, thecontrollers may be independent from one another. The humidifiercontroller 8 b may be an independent unit configured for use with anytype of gas source.

In some embodiments, the blower controller 8 a and the humidifiercontroller 8 b are in a master-servant relationship—generally this couldrefer to the capability of one of the controller to control thefunctions of the other controller. In an alternative embodiment, theblower controller 8 a and the humidifier controller 8 b are in a peerrelationship—generally this could refer to capability of each controllerto function independently of the other.

In some embodiments, the control system 8 receives user input signalsvia user controls 11 located on either the humidifier base unit 21, oron the blower unit 3, or both. In some embodiments the controller 8 alsoreceives input from sensors located at various points throughout thesystem 1. In alternative embodiments, the humidifier may include avertical wall or spine having user controls 11 located on the spine. Theuser controls may be positioned above the humidification chamber 5 andthe heater plate 12. This would provide the user with the ability tointeract with the user controls with minimal risk of touching the heaterplate 12.

The sensors and their locations will be described in more detail below.In response to the user input from controls 11, and the signals receivedfrom the sensors, the control system 8 determines a control output whichin some embodiments sends signals to adjust the power to the humidifierchamber heater plate 12 and the speed of the fan 13. The programmingwhich determines how the controller determines the control output willbe described in more detail below.

A schematic view of the user 2 receiving air from an integratedblower/humidifier system 100 according to a second form of thedisclosure is shown in FIG. 5 . The system operates in a very similarmanner to the modular system 1 shown in FIG. 4 and described above,except that the humidifier chamber 105 has been integrated with theblower unit 103 to form an integrated unit 110. A pressurized gasesstream is provided by fan unit 113 located inside the casing of theintegrated unit 110. The water 120 in the humidifier chamber 105 isheated by heater plate 112 (which is an integral part of the structureof the blower unit 103 in this embodiment). Air enters the humidifierchamber 105 via an entry port 123, and exits the humidifier chamber 105via exit port 109. The gases stream is provided to the user 2 via adelivery conduit 106 and an interface 107. The controller 108 iscontained within the outer shell of the integrated unit 100. In theillustrated embodiment, the controller 108 is a single controller thatcontrols the heater plate 112 and the operation of the blower unit 103based on one or more sensor inputs. The controller 108 may compriseindividual software or hardware modules to control the blower unit 103and the heater plate 112. User controls 111 are located on the outersurface of the unit 100.

A schematic view of the user 2 receiving air from a further form ofbreathing assistance system 200 is shown in FIG. 6 . The system 200 canbe generally characterized as a remote source system, and receives airfrom a remote source via a wall inlet 1000.

The wall inlet 1000 is connected via an inlet conduit 201 to a controlunit 202, which receives the gases from the inlet 1000. The control unit202 has sensors 250, 260, 280, 290 which measure the humidity,temperature and pressure and flow respectively of the incoming gasesstream.

The gases flow is then provided to a humidifier chamber 205, with thegases stream heated and humidified and provided to a user in a similarmanner to that outlined above. It should be noted that when ‘humidifierunit’ is referred to for a remote source system such as the system 200,this should be taken to mean as incorporating the control unit 202—thegases from the remote source can either be connected directly to aninlet, or via the control unit 202 (in order to reduce pressure orsimilar), but the control unit and the humidifier chamber should beinterpreted as belonging to an overall ‘humidifier unit’.

In some embodiments, the system 200 can provide O₂ or an O₂ fraction tothe user. The system may provide O₂ to the user by having the centralsource as an O₂ source. In an alternative embodiment, the system mayprovide O₂ by blending atmospheric air with incoming O₂ from the centralsource. The blending of atmospheric air and incoming O₂ may occur via aventuri 90 or similar located in the control unit 202.

The control unit 202 may also have a valve 211 or a similar mechanism toact as a flow control mechanism to adjust the flow rate of gases throughthe system 200. Additionally, the control unit may also have a pluralityof valves to control the flow rate of gases through the system 200. Insome embodiments, the valve 211 operation may be controlled by thecontroller 9. In an alternative embodiment, the valve 211 operation maybe controlled by an additional controller located within the controlunit 202.

Sensors

The modular and integrated systems 1, 100 and 200 shown in FIGS. 4, 5and 6 have sensors located at points throughout the system. These willbe described below in relation to the breathing assistance system 1.

In an embodiment, the modular system 1, as shown in FIG. 4 , has atleast the following sensors in the following locations:

1) An ambient temperature sensor 60 located within, near, or on theblower casing, configured or adapted to measure the temperature of theincoming air from atmosphere. Temperature sensor 60 may be located inthe gases stream after (downstream of) the fan unit 13, and as close tothe inlet or entry to the humidifier chamber as possible.

2) A humidifier unit exit port temperature sensor 63 located either atthe chamber exit port 9, or located at the apparatus end (opposite tothe patient end) of the delivery conduit 6. Outlet temperature sensor 63is configured or adapted to measure the temperature of the gases streamas it exits chamber 5 (in either configuration the exit port temperaturesensor 63 can be considered to be proximal to the chamber exit port 9).

Similarly, sensors are arranged in substantially the same locations inthe integrated system 100 shown in FIG. 5 and the system 200 of FIG. 6 .For example, for the integrated system of FIG. 5 , an ambienttemperature sensor 160 is located within the blower casing in the gasesstream, just before (upstream of) the humidifier chamber entry port 123.A chamber exit port temperature sensor 163 is located either at thechamber exit port 109 and is configured to measure the temperature ofthe gases stream as it exits chamber 105 (in either configuration theexit port temperature sensor 163 can be considered to be proximal to thechamber exit port 109). Alternatively, this sensor can be located at theapparatus end (opposite to the patient end) of the delivery conduit 106,for either embodiment. A similar numbering system is used for thebreathing assistance system shown in FIG. 6 —ambient temperature sensor260, fan unit 213, chamber exit port temperature sensor 263 located atthe chamber exit port 209, etc.

In an embodiment, the breathing assistance system 1 (and 100, 200) has aheater plate temperature sensor 62 located adjacent to the heater plate12, configured to measure the temperature of the heater plate. Thebreathing assistance system(s) having a heater plate temperature sensormay be used as it gives an immediate indication of the state of theheater plate. This sensor should be in the heat path between the sourceof the heat and the reservoir. So, for example, a sensor on a conductiveplate that contacts the water chamber on one side and has a heater onthe other side may be used.

In an embodiment, the systems have a flow sensor located upstream of thefan unit 13 and configured to measure the gases flow. The location forthe flow sensor can be upstream of the fan unit, although the flowsensor can be located downstream of the fan, or anywhere elseappropriate. In some embodiments, the flow sensor may be located at theoutlet 9 adjacent to a temperature sensor 63. The flow sensor can formpart of the system, but it is not absolutely necessary for a flow sensorto be part of the system.

In an embodiment, the system may include a temperature sensor 63 locatedat the outlet 9 to the humidification chamber 5. In an alternativeembodiment, the temperature sensor 63 may be located at the inlet 23 tothe humidification chamber 5. The temperature sensor 63 may beconfigured to also function as a flow sensor based on the polarity ofvoltage applied to the temperature sensor 63 or the level of voltageapplied to the temperature sensor 63.

The layout and operation of the breathing assistance system 1 will nowbe described below in detail. The operation and layout of the systems100 and 200 is substantially the same, and will not be described indetail except where necessary.

For the breathing assistance system 1, the readings from all of thesensors are fed back to the control system 8. The control system 8 alsoreceives input from the user controls 11.

Further Alternative Sensor Layouts

In a variant of the apparatus and method outlined above, the system(system 1 or system 100 or system 200) also has additional sensors asoutlined below.

3) A patient end temperature sensor 15 (or 115 or 215) is located at thepatient end of the delivery conduit 6 (or alternatively in or on theinterface 7). That is, at or close to the patient or point of delivery.When read in this specification, ‘patient end’ or ‘user end’ should betaken to mean either close to the user end of the delivery conduit (e.g.delivery conduit 6), or in or on the patient interface 7. This appliesunless a specific location is otherwise stated. In either configuration,patient end temperature sensor 15 can be considered to be at or close tothe user or patient 2.

Operational State Determination

According to some embodiments, the respiratory assistance systemincorporates a routine configured to select the appropriate water outdetection method to determine whether the humidification chamber 5requires the addition of water based on the operational state of thesystem. The operational state relates to a user selected therapy modefor the system and a gases flow rate. This routine, as discussed infurther detail below and may be run at any suitable time interval. Insome embodiment, the routine is executed every 10 minutes. This allowsthe heater plate to adequately cool in the event that an active test hasbeen previously executed. However, in alternative embodiments, theroutine could be executed every few seconds or every few milliseconds.The routine is illustrated in FIGS. 1 a and 1 b . FIGS. 1 a and 1 billustrate alternative embodiments for control of the system at thefourth operational state.

While the decision steps are described in a sequential manner, thesystem may perform the steps in a different sequence or concurrently, aswell. As illustrated in step 1001, a controller 8 receives informationrelating to the system's therapy mode. The controller 8 then proceeds todetermine the system's flow rate at step 1002. The flow rate may bedetermined through a flow sensor positioned on the humidificationchamber 5, specifically at either the inlet 23 or outlet ports 9.Alternatively, the flow sensor may be positioned downstream to the fanunit 13 associated with the blower unit 3. The controller 8 utilizes thereceived therapy mode and flow rate information to determine thesystem's operational state. Based on the system's operational mode andflow rate, the controller 8 selects the appropriate water out detectionmethod.

Cold Start Operational State

At step 1003, the controller 8 determines whether the system is in acold start operational state. After startup, the system is determined tobe in a cold start operational state until: (i) the heater platetemperature exceeds a defined temperature threshold, (ii) a defined timethreshold since startup of the system is satisfied, (iii) thetemperature at the chamber outlet exceeds a defined temperaturethreshold, and/or (iv) the temperature at the patient end exceeds adefined temperature threshold. The heater plate temperature, chamberoutlet temperature and patient end temperature can be determined bytheir respective temperature sensors, such as for example temperaturesensors 62, 63, and 15. The defined temperature thresholds of the heaterplate, the chamber outlet, and patient end can be temperatures greaterthan 30 degrees Celsius, such as, for example 35 degrees Celsius, 37degrees Celsius, 40 degrees Celsius, 42 degrees Celsius, and/or anotherdefined temperature that is a sufficient temperature for respectivecomponent after startup of the system. Each defined temperaturethreshold of the heater plate, the chamber outlet, and patient end canbe separately defined. For example, in a preferred embodiment, theheater plate temperature threshold is 40 degrees Celsius, the chamberoutlet temperature threshold is 37 degrees Celsius, and the patient endtemperature threshold is 40 degrees Celsius. In some embodiments, thesystem chamber outlet includes a defined flow rate threshold and atemperature threshold. The flow rate threshold can be any non-zero flowrate, such as, for example about or greater than 0.5 L/min, about orgreater than 3 L/min, or another non-zero flow rate. For example, thechamber outlet temperature threshold can be 37 degrees Celsius with aflow rate threshold of 3 L/min. The defined time threshold for the timemeasured since startup of the system can be 2 minutes, 5 minutes, 10minutes, 20 minutes, and/or any other defined time period that providessufficient time for the heater plate to heat up after startup of thesystem. The cold start operational state is not dependent on therapymode or flow rate. In some alternative embodiments, the cold startoperational state can be dependent at least in part on the flow rate.

If the controller 8 determines the system satisfies the criteria to bein the cold start operational state, the controller 8 proceeds to anactive water out detection method at step 1004. If the active water outdetection method returns a water out condition, the alarm is activatedwith a setup error and/or a water out alarm. If the controller 8determines the system does not satisfy the criteria to be in cold startoperational state, the controller 8 proceeds to the step 1005. In someembodiments, the default operational state after startup of the systemis the cold start operational state. The system will stay in the coldstart operational state until one of the criteria for exiting the coldstart operational mode has been satisfied. For example, the system willstay in the cold start operational mode until the time threshold issatisfied or one of the temperatures of the heater plate, the chamberoutlet, or the patient inlet exceed their respective temperaturethresholds.

First Operational State

At step 1005, the controller 8 determines whether the system is in afirst operational state. The system is determined to be in a firstoperational state (or “no flow” state) when the flow rate is between 0-3L/min for any selected therapy mode. If the controller 8 determines thesystem satisfies the criteria to be in a first operational state, thewater out alarm is disabled at step 1006. At this low flow rate, falsealarms can be common because the water level will not decrease rapidlyduring a low flow state. The alarm can be disabled without seriousconcern. When the alarm is disabled, the controller 8 may return back tostep 1001. However, if the controller 8 determines the system does notsatisfy the criteria to be in a first operational state, the controller8 proceeds to step 1007.

Second Operational State

At step 1007, the controller 8 determines whether the system is in asecond operational state. The system is determined to be in a secondoperational state when the system is in either an invasive therapy modeor an Optiflow® therapy mode and the flow rate is determined to be at amedium or high flow rate. The flow rate level is based on thresholdsthat are provided to the system.

When the controller 8 determines that the system satisfies the criteriato be in a second operational state, the controller 8 proceeds to apassive water out detection method at step 1008. If the passive waterout detection method returns a water out condition, the alarm isactivated without running an active water out detection method. However,if the controller 8 determines the system does not satisfy the criteriato be in a second operational state, the controller 8 proceeds to thefollowing step.

Third Operational State

At step 1009, the controller 8 determines whether the system is in athird operational state. The system is determined to be in a thirdoperational state when the system is in either an invasive therapy modeor an Optiflow® therapy mode and the flow rate is determined to be at amedium or low flow rate.

When the controller 8 determines that the system satisfies the criteriato be in a third operational state, the controller 8 proceeds to apassive water out detection method at step 1010. The passive water outdetection method determines whether there is a water out condition atstep 1011. If the passive water out detection method returns a water outcondition, then the controller proceeds to an active water out detectionmethod at step 1012. As described in further detail below, an activewater out detection method is run in conjunction with the passive waterout detection method to decrease the likelihood of a false positivealarm for therapy modes with lower set points. If the active water outdetection method returns a water out condition, the alarm is activated.However, if the active water out detection method does not return awater out condition, the controller 8 terminates the sequence andreinitiates the routine at the suitable time interval.

Additionally, if the controller 8 determines the system does not satisfythe criteria to be in a third operational state, the controller 8proceeds to the following step.

Fourth Operational State

At step 1013, the controller 8 determines whether the system is in afourth operational state. The system is determined to be in a fourthoperational state when the system is in a non-invasive therapy mode.

When the controller 8 determines that the system satisfies the criteriato be in a fourth operational state, the controller 8 proceeds to apassive water out detection method at step 1010. If the passive waterout detection method returns a water out condition, then the controller8 proceeds to an active water out detection method at step 1012. If theactive water out detection method returns a water out condition, thealarm is activated.

However, if the active water out detection method does not returns awater out condition or the controller 8 determines the system does notsatisfy the criteria to be in a fourth operational state, the controller8 terminates the sequence and reinitiates the routine at the suitabletime interval.

With reference now to FIG. 1 b , an alternative embodiment for thefourth operational state is illustrated. In FIG. 1 b , when thecontroller 8 determines that the system satisfies the criteria to be ina fourth operational state, the controller 8 proceeds to a time-basedactive water out detection method at step 1014. At step 1014, thecontroller 8 determines whether a defined time period has elapsed sincethe previous active water out detection method was activated or sincethe system entered the non-invasive therapy mode. If the controller 8determines that the defined time period has elapsed, then the controller8 proceeds to an active water out detection method at step 1012. Thedefined time period can be any defined time interval, such as, forexample 15 minutes, 20 minutes 30 minutes, one hour, and the like. Ifthe time period has not elapsed, the controller 8 may return back tostep 1001. In some embodiments, the controller 8 will continue toexecute the active water detection method at each defined time interval.

Step 1001 can represent ongoing receipt of the information relating tothe system's therapy mode according to the system conditions. Thisongoing process aims to ensure that the humidification chamber 5contains sufficient water to keep the delivered gases temperature andhumidity at or close to the preferred level. As an ongoing process, theroutine monitors for a possible water out condition. However, it shouldbe noted that the routine need not continuously monitor for a possiblewater out condition. The routine may be run at suitable intervalsdepending on the system requirements.

Alternative Routine Embodiment

As described in further detail below, in some embodiments, the passivewater out detection method may be continuously running since thisdetection method comprises a calculation based on sensor data collectedduring the normal course of operation. As such, the method does notimpact humidifier operation.

Accordingly, in an alternative embodiment, as illustrated in FIG. 2 ,the initiation of the routine, at step 2002, may be triggered based on afirst water out condition detected by a continuously run passive waterout detection method, as shown in step 2001. The system may theninitiate a routine to select the appropriate method capable ofaccurately determining to determine whether the humidification chamber 5is dry based on the operational state of the system, similar to theprevious embodiment discussed above.

Water Out Detection Methods

Various water out detection methods are described below which are usedto determine if a water out condition is present. Each method is usedunder certain conditions, and the system's routine selects the mostappropriate water out detection method based on system's operationalstate, as previously described in further detail above. Once anappropriate water out detection method is selected, the system utilizesone of the methods described below to determine the existence ornon-existence of a water out condition.

Passive Water Out Detection Method

According to the present disclosure, a passive water out detectionmethod determines if a water out condition is present. With reference toFIG. 2 , according to an embodiment, the controller 8 evaluates afunction of the heater plate power, the heater plate temperature, andthe chamber outlet temperature on a continuing basis during normal useof the apparatus. The passive water out detection method is constantlyrunning since it does not impact the humidifier operation. The passivewater out detection method runs a calculation of the estimated waterlevel based on sensor data collected during the normal course ofoperation.

The controller 8 determines the potential for a water out condition whenthe result of the function below varies from a base line thresholdlevel. The function is a ratio of the chamber outlet temperature fromsensor 63 (or 163 or 263) and the heater plate power, as represented bythe heater plate duty cycle.

The passive water out detection method estimates the current water levelusing at least the heater plate power, heater plate temperature, andchamber outlet temperature. In some embodiments, no coefficients orweighting factors are used. The passive water out detection methodestimates water level according to the following formula:

${{Estimated}{Water}{Level}} = \frac{{Heater}{Plate}{Power}}{{{Heater}{Plate}{Temperature}} - {{Chamber}{Outlet}{Temperature}}}$

As the humidification chamber 5 dries, the amount of power required tomaintain the same chamber outlet temperature decreases, which is usefulfor detecting a water out condition. When the estimated water leveldrops below a pre-defined threshold for some time, a water out alarm israised.

The threshold is dependent on the flow rate and can be determinedempirically. With water in the chamber, the system is allowed to reachsteady state regarding flow rates within the operating range. Then,without water in the chamber, the system is tested with the same flowrates. The result is two values, a water in value and a water out value.In some embodiments, the threshold is set half way between these twovalues. As the user selects different therapy modes, the threshold valuecan be adjusted according to the selected therapy mode's particular setpoint value.

Since the estimated water level is based on heater plate power, whichmay fluctuate due to pulsatile flow, controller stability, etc., in someembodiments, a timer is used to wait a set period of time with theestimated water level below the threshold value before activating thealarm. In some embodiment, this is set to 15 minutes for low flow ratesand 10 minutes for higher flow rates. There is also a separate settlingtimer for preventing false triggers due to set point changes, flow ratechanges, etc. In some embodiments, this is set to 20 minutes.

In some embodiments, once the humidification chamber 5 is filled withwater following a water out condition alarm, the alarm will bedeactivated when the estimated water level rises above the threshold.

Active Water Out Detection

According to the present disclosure, in certain circumstances, an activewater out detection method of the water out condition is made inresponse to the passive water out detection method determining a waterout condition. According to some embodiments, during the active waterout detection method, the controller 8 takes control of the humidifierpower input, adjusts the heater plate power input and observes thetemperature response of the heater plate 12. This active water outdetection method is implemented in certain circumstances to confirm thewater out condition when the passive water out detection method returnsa possible water out condition.

In some embodiments, the passive water out detection method may be usedwithout the active test; however, this may sacrifice some accuracy atlow flow rates. In alternative embodiments, the active test may be usedwithout the passive test; however, this may be more intrusive to thedelivery of therapy and the execution of other modules, such as the lowtemperature alarm.

In some embodiments, the active water out detection method may be usedto confirm a water out condition since a passive water out detectionmethod may falsely determine a water out condition under certainoperational states. These states include the third and fourthoperational states, as discussed above. The likelihood of the passivewater out detection method returning a false positive increases forlower set points because the denominator of the estimated water levelratio, as described above, gets too close to zero. This occurs becausethe heater plate temperature is also lowered, causing the twodenominator values to become closer in range. This occurs since both theheater plate temperature and the chamber outlet temperature are closerto ambient. Therefore, the heater plate does not have to work as hard toachieve the chamber outlet target temperature.

According to the present disclosure, after the passive water outdetection method determines a water out condition, the controller 8begins performing the active water out detection method when the systemis in the third or fourth operational states.

During an active test, the controller 8 takes control of the heaterplate feedback mode and duty cycle calculations in accordance with theroutine described below. As illustrated in FIG. 3 , the active water outdetection method involves pulsing the heater plate 12 with a fixed powerfor a short duration and observing the rise of the heater plate 12temperature. When the humidification chamber 5 is dry, the effectivethermal mass of the heater plate is reduced and a higher peak heaterplate temperature is expected. Upon completion of the active water outdetection method, the controller 8 transitions to step 3001 and controlof the heater plate feedback mode and duty cycle calculations is thenreturned to the normal heater plate control algorithm and PI controller.

As illustrated in FIG. 3 , according to the routine, the controller 8performs the following active water out detection method describedbelow.

As shown in step 3001, the system waits for a trigger resulting from thepassive water out detection method returning a water out condition whilethe system is under a third or fourth operational state. In this state,the heater plate control mode is normal and uses chamber outletfeedback. If the system receives a water out condition trigger, as shownin step 3002, the system is due for an active water out detection testand will transition to the next step.

At step 3003, the controller 8 controls the heater plate temperature toa baseline, so that the starting condition of the test is controlled. Toachieve a baseline, the system switches off, reduces power supplied orprovides constant power to the heater plate 12 at a low enough level toachieve the desired baseline level. The heater plate temperature mustthen remain within 0.1° C. for 15 seconds prior to the controller 8transitioning to the next step.

At step 3004, the controller 8 adjusts the heater plate's duty cycle toapply 150 W to the heater plate 12 for 10 seconds. The controller 8 thentransitions to the next step.

At step 3005, the controller 8 disables the heater plate power andmonitors the temperature of the heater plate 12 for maximum heater platetemperature with a heater plate sensor. The temperature curve ismonitored until a maximum temperature is reached.

The maximum heater plate temperature is determined by any suitablemethod at step 3006. A method of determining the maximum temperature isby taking a first derivative of the temperature signal and indicatingthe maximum temperature when the derivative is equal to 0.Alternatively, the system can wait until there is a reduction intemperature and utilizing the measurement immediately before thereduction as the maximum temperature. As soon as the maximum heaterplate temperature is reached, the system transitions to the next step.

At step 3007, the system determines whether the maximum heater platetemperature exceeds a predetermined threshold. The threshold is set athalfway between the estimated heater plate temperature rise when thechamber is full and the estimated heater plate temperature rise when thechamber is dry. The mathematical formulas for the calculation of thethreshold value are included below:

Heater Plate Temperature Threshold=0.5*Estimated Heater PlateTemperature Full+(1−0.5)*Estimate Heater Plate Temperature Dry

Estimated Heater Plate Temperature Full=5.377−0.052*Heater PlateTemperature Baseline—0.017*Filtered Flow Rate

Estimated Heater Plate Temperature Dry=6.970−0.040*Heater PlateTemperature Baseline—0.017*Filtered Flow Rate

The threshold can be adjusted for ambient conditions and flow rate,among other parameters. In some alternative embodiments, the system mayautomatically adjust thresholds based on changes in other parameters.Alternatively, the system may have a preset number of stored thresholdsfor various environmental parameters.

If the maximum heater plate temperature or the measured temperatureafter 10 seconds does not exceed a threshold level, then the controller8 determines that the water is not out. The controller 8 transitions tostep 3001 and waits for the next request for an active water outdetection test. In some embodiments, the controller 8 may do nothingprior to transitioning to step 3001. Alternatively, the controller 8 maymessage the user stating that there is enough water before returning tostep 3001.

As soon as the maximum heater plate temperature or the measuretemperature after 10 seconds exceeds the threshold level, the controller8 activates the alarm at step 3008. The alarm can be a visual alarm, amessage, an animation, or an audible alarm. After the alarm isactivated, the controller 8 may transition to step 3001 and wait for thenext request for an active water out detection test.

An example of this monitoring function is illustrated in FIG. 7 . Thisgraph shows data captured during a test of the routine selecting theappropriate water out detection method. Moving in time from left toright, the heater plate power (shown as HPPower) spikes at system startup and then settles to a steady state, as do the heater platetemperature, the chamber outlet temperature, and the filtered waterlevel, previously referred to as the estimate water level.

A first phase is reached as the water in the humidification chamber 5runs out. At this moment, the baseplate is dry but the chamber outlettemperature sensor is still wet from condensation. The temperaturesensor returns lower values even though the gas temperature is notdropping. This occurs because the wet temperature sensor measuring drygas introduces error. The heater plate power increases to compensate thedecrease in the temperature values. As a result, the heater platetemperature rises as well, but faster than usual due to the absence ofwater on the baseplate. The filtered water level starts to drop becauseof this change in the ratio.

A second phase is reached after the temperature sensor is dried and theerror is no longer present. The heater plate power decreasescorrespondingly, but the heater plate temperature continues to risebecause the air above the baseplate does not absorb as much heat aswater would have. This causes the filtered water level to drop even moresteeply as the heater plate power and heater plate temperature continueto diverge.

A third phase is reached when the filtered water level drops below thewater out threshold. In this example, the therapy mode is set tonon-invasive or the flow rate is low to medium, which causes the activewater out detection method to be initiated. Each of the spikes in heaterplate power reflects an execution of the test (i.e., the state machinetransitions to step 3004). After the third spike, the humidificationchamber 5 is refilled with water, causing the heater plate temperatureto drop drastically. This, in turn, causes the heater plate powerincreases to heat the added cold water.

System Therapy Modes

According to the present disclosure, the respiratory assistance systemmay be placed in one of several therapy modes. The selected therapy modealters certain set point and threshold values during the controller's 8determination of the appropriate water out detection method. Inparticular, the therapy mode may alter the specific gases flow rate ofthe system.

In some embodiments, the therapy modes may be selected from one ofeither an invasive mode, a non-invasive mode, or an Optiflow® mode. TheOptiflow® mode is utilized when the application requires a high flowrate through an unsealed interface.

As described, each therapy mode has individualized set points. In someembodiments, the non-invasive mode may comprise set points of 31degrees, 29 degrees and 27 degrees Celsius. The Optiflow® mode maycomprise set points of 37 degree, 35 degree and 33 degrees Celsius. Theinvasive mode may comprise set points of 37 degrees Celsius.

In some embodiments, the system may comprise a user interface configuredto permit a user to select the respective therapy mode.

Gases Flow Rates

According to the present disclosure, the respiratory assistance systemmay also be configured to provide a variety of gases flow rates. Theselected flow rate alters the system's determination of the appropriatewater out detection method. In particular, the flow rate may alter theparticular system operational state of the system.

In some embodiments, the flow rate may be selected from one of either ano flow rate, a low flow rate, a medium flow rate, or a high flow rate.As described, each flow rate has an individualized classification range.In some embodiments, the no flow rate may comprise a rate between 0L/min-3.5 L/min. The low flow rate may comprise a rate between 3 L/min-7L/min. The medium low flow rate may comprise a rate between 5 L/min-15L/min. The medium high flow rate may comprise a rate between 13 L/min-35L/min. The high flow rate may comprise a rate greater than 30 L/min.

The ranges of each flow rate category can overlap with other categories.In order to move from one flow rate category to the next, the flow rateneeds to exceed the upper limit of the category or drop below the lowerlimit of the category. For example, if the current flow rate is the lowflow category, the flow rate will need to exceed 7 L/min in order tomove into the medium low category. Similarly, in order to move back downto the low category once within the medium low category, the flow ratewill need to drop below 5 L/min. The overlapping ranges can help toprevent constantly switching categories for flow rates that arefluctuating close to a threshold.

Design Considerations

Baseline Temperature

Since the heater plate temperature increase is dependent on the baselinetemperature, the test range for the threshold design should include theminimum and maximum expected heater plate temperatures within theintended operating range. To minimize effects on passive alarms andtherapy delivery, the baseline temperature should be close to theoperating heater plate temperature. If there is an enthalpy concern,then the baseline temperature should be lower than the operating heaterplate temperature, but this may increase test cycle time.

Flow Rate

The same analysis described under Baseline Temperature applies for flowrate, as well. The test range should include the expected operatingrange.

Open Loop Duty Cycle

An open loop duty cycle is applied, which gives a good rectangular pulsein power and is not affected by the controller 8. The duty cycle isbased on the measured mains voltage from the PMIC, the measured heaterplate resistance, and the desired power.

Power Applied

In some embodiments, 150 W is selected because the heater plate is ableto deliver it even if the mains voltage is reduced by 10% (given thenominal heater plate power is 200 W). If the delivered power werehigher, the heater plate may not be able to deliver the same power whenconnected to a lower mains voltage. If it were lower, the heater platetemperature rise may be reduced which could increase the possibility offalse alarms.

Power Application Time

In some embodiments, 10 seconds is selected so the effect from timingjitter can be reduced while minimizing the possibility of generatingexcessive humidity. (Note: if the timer implementation changes andaffects the duration of the pulse, then the threshold needs to bere-determined.)

Detection Criteria

Maximum heater plate temperature is used as the detection metric becauseof consistency, good signal-to-noise ratio between dry and wet chambers,low computational complexity, and faster test cycle time.

Minimum Time in Step 3005

Due to the delay between the application of power and the heater platetemperature response, the controller 8 stays in step 3005 long enough toobserve an increase in heater plate temperature before exiting when thetemperature drops below the maximum.

Potential Interruption

Since the test takes a non-negligible amount of time to complete, it ispossible that external events may affect the outcome. Possible eventsinclude: a water refill, a flow rate or pattern change, a therapy modechange, a set point change (due to user or humidity compensation), aninspiratory circuit or sensor cartridge disconnection, and a power on oroff.

In the event of a water refill, the heater plate temperature willdecrease. However, this is good as a lower temperature indicates wateris present.

Interaction with Low Temperature Alarm

Since the active water out detection method interrupts normal heating,the heater plate and chamber outlet temperatures will be affected. Theroutine attempts to minimize this effect by setting the baselinetemperature close to the current operating heater plate temperature. Anactive water out detection method is expected to be completed wellwithin 10 minutes, thus the low temperature alarm (which takes between10 and 60 minutes to trigger, depending on the therapy and set point)should not raise a false alarm.

Timeout and Return to Default State

If the system is unable to satisfy the conditions for a statetransition, a timeout will occur and the state will return to step 3001.In an embodiment of the device, the timeout values may be as follows:

Step 3003 timeout=15 minutes

Step 3004 timeout=15 seconds

Step 3005 timeout=5 minutes

Not Enough Energy Delivered

Due to timing or lower than expected mains voltage, the system may notdeliver the required power over time. Power measurements made by thePMIC will be recorded to assess the energy pulse delivered during theactive testing phase. In some embodiments, if the power isunder-delivered or over-delivered, the system will retry 3 times. If allretries fail, the system will disable the active water out detectionmethod (because it affects the passive water out detection method) andfall back to the passive water out detection method.

Test Duration

Test duration is minimized to reduce the disruption to normal therapy byallowing an active water out detection method to start at variousbaseline heater plate temperatures.

Examples of respiratory humidification systems and associated componentsand methods have been described with reference to the figures. Thefigures show various systems and modules and connections between them.The various modules and systems can be combined in variousconfigurations and connections between the various modules and systemscan represent physical or logical links. The representations in thefigures have been presented to clearly illustrate the principles anddetails regarding divisions of modules or systems have been provided forease of description rather than attempting to delineate separatephysical embodiments. The examples and figures are intended toillustrate and not to limit the scope of the inventions describedherein. For example, the principles herein may be applied to arespiratory humidifier as well as other types of humidification systems,including surgical humidifiers. The principles herein may be applied inrespiratory applications as well as in other scenarios for determiningwhether water is available within a respiratory system.

As used herein, the term “processor” refers broadly to any suitabledevice, logical block, module, circuit, or combination of elements forexecuting instructions. For example, the controller 8 can include anyconventional general purpose single- or multi-chip microprocessor suchas a Pentium® processor, a MIPS® processor, a Power PC® processor, AMD®processor, ARM® processor, or an ALPHA® processor. In addition, thecontroller 122 can include any conventional special purposemicroprocessor such as a digital signal processor or a microcontroller.The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), or other programmable logicdevice, discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein, or can be a pure software in the main processor. For example,logic module 504 can be a software-implemented function block which doesnot utilize any additional and/or specialized hardware elements.Controller 8 can be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a combination of amicrocontroller and a microprocessor, a plurality of microprocessors,one or more microprocessors in conjunction with a DSP core, or any othersuch configuration.

Data storage can refer to electronic circuitry that allows data to bestored and retrieved by a processor. Data storage can refer to externaldevices or systems, for example, disk drives or solid state drives. Datastorage can also refer to fast semiconductor storage (chips), forexample, Random Access Memory (RAM) or various forms of Read Only Memory(ROM), which are directly connected to the communication bus or thecontroller 8. Other types of data storage include bubble memory and corememory. Data storage can be physical hardware configured to store datain a non-transitory medium.

Although certain embodiments and examples are disclosed herein,inventive subject matter extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses, and tomodifications and equivalents thereof. Thus, the scope of the claims orembodiments appended hereto is not limited by any of the particularembodiments described herein. For example, in any method or processdisclosed herein, the acts or operations of the method or process can beperformed in any suitable sequence and are not necessarily limited toany particular disclosed sequence. Various operations can be describedas multiple discrete operations in turn, in a manner that can be helpfulin understanding certain embodiments; however, the order of descriptionshould not be construed to imply that these operations are orderdependent. Additionally, the structures described herein can be embodiedas integrated components or as separate components. For purposes ofcomparing various embodiments, certain aspects and advantages of theseembodiments are described. Not necessarily all such aspects oradvantages are achieved by any particular embodiment. Thus, for example,various embodiments can be carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other aspects or advantages as can also be taughtor suggested herein.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments. As used herein, the terms “comprises,”“comprising,” “includes,” “including,” “has,” “having” or any othervariation thereof, are intended to cover a non-exclusive inclusion. Forexample, a process, method, article, or apparatus that comprises a listof elements is not necessarily limited to only those elements but mayinclude other elements not expressly listed or inherent to such process,method, article, or apparatus. Also, the term “or” is used in itsinclusive sense (and not in its exclusive sense) so that when used, forexample, to connect a list of elements, the term “or” means one, some,or all of the elements in the list. Conjunctive language such as thephrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be either X, Y or Z. Thus, suchconjunctive language is not generally intended to imply that certainembodiments require at least one of X, at least one of Y and at leastone of Z each to be present. As used herein, the words “about” or“approximately” can mean a value is within ±10%, within ±5%, or within±1% of the stated value.

Methods and processes described herein may be embodied in, and partiallyor fully automated via, software code modules executed by one or moregeneral and/or special purpose computers. The word “module” refers tologic embodied in hardware and/or firmware, or to a collection ofsoftware instructions, possibly having entry and exit points, written ina programming language, such as, for example, C or C++. A softwaremodule may be compiled and linked into an executable program, installedin a dynamically linked library, or may be written in an interpretedprogramming language such as, for example, BASIC, Perl, or Python. Itwill be appreciated that software modules may be callable from othermodules or from themselves, and/or may be invoked in response todetected events or interrupts. Software instructions may be embedded infirmware, such as an erasable programmable read-only memory (EPROM). Itwill be further appreciated that hardware modules may comprise connectedlogic units, such as gates and flip-flops, and/or may comprisedprogrammable units, such as programmable gate arrays, applicationspecific integrated circuits, and/or processors. The modules describedherein can be implemented as software modules, but also may berepresented in hardware and/or firmware. Moreover, although in someembodiments a module may be separately compiled, in other embodiments amodule may represent a subset of instructions of a separately compiledprogram, and may not have an interface available to other logicalprogram units.

In certain embodiments, code modules may be implemented and/or stored inany type of computer-readable medium or other computer storage device.In some systems, data (and/or metadata) input to the system, datagenerated by the system, and/or data used by the system can be stored inany type of computer data repository, such as a relational databaseand/or flat file system. Any of the systems, methods, and processesdescribed herein may include an interface configured to permitinteraction with users, operators, other systems, components, programs,and so forth.

It should be emphasized that many variations and modifications may bemade to the embodiments described herein, the elements of which are tobe understood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.Further, nothing in the foregoing disclosure is intended to imply thatany particular component, characteristic or process step is necessary oressential.

1-29. (canceled)
 30. A method of determining a water out condition for arespiratory assistance system, the method comprising: receiving datarelating to a selected therapy mode; receiving a flow data; determiningan operational state based on at least one of a temperature of a heater,a temperature at an outlet of a humidification chamber, or the selectedtherapy mode and flow rate of gases; and selecting at least one waterout detection method based on the operational state.
 31. The method ofdetermining a water out condition of claim 30, wherein determining theoperational state is based on a temperature set point and a flow rate ofgases, wherein the temperature set point is based on the selectedtherapy mode.
 32. The method of determining a water out condition ofclaim 30, the determining the operational state comprising apredetermined relationship between therapy mode and flow rate of gases.33. The method of determining a water out condition of claim 30 furthercomprising: detecting the flow rate by a flow sensor; receiving the datarelating to a selected therapy mode from a user interface; and relatinga temperature set point to a temperature sensor located at ahumidification chamber, a conduit, or both.
 34. The method ofdetermining a water out condition of claim 30, wherein the selectedtherapy mode is selected from a predetermined list comprising: aninvasive mode; a non-invasive mode; and a high flow, unsealed mode,wherein the high flow, unsealed mode comprises a high flow rate throughunsealed interface.
 35. The method of determining a water out conditionof claim 34, wherein the selected therapy mode comprises a plurality ofset points.
 36. The method of determining a water out condition of claim34, the non-invasive mode comprising set point of 31 degrees, 29degrees, and 27 degrees Celsius.
 37. The method of determining a waterout condition of claim 30, the operational state comprising a startupoperational state relating to a temperature of the heater below adefined temperature threshold or the temperature at the outlet of thehumidification chamber below a defined temperature threshold, a firstoperational state relating to a no flow rate or low flow rate, a secondoperational state relating to a therapy mode having a high set point anda high flow rate, a third operational state relating to a therapy modehaving a low set point, a fourth operational state relating to a therapymode having a high set point and low flow rate or medium flow rate. 38.The method of determining a water out condition of claim 37, the highset point having a temperature above 31 degrees Celsius, and the low setpoint having a temperature between 25 degrees and 31 degrees Celsius.39. The method of determining a water out condition of claim 37, whereinthe defined temperature threshold of the heater is greater than or equal30 degrees Celsius.
 40. (canceled)
 41. The method of determining a waterout condition of claim 37, wherein the defined temperature threshold ofthe outlet of the humidification chamber is greater than or equal to 30degrees Celsius.
 42. (canceled)
 43. The method of determining a waterout condition of claim 37, the no flow rate having a rate between 0l/min-3.5 l/min, the low flow rate having a rate between 3 l/min-7l/min, the medium flow rate having a rate between 5 l/min-15 l/min, andthe high flow rate having a rate between 13 l/min-35 l/min.
 44. Themethod of determining a water out condition of claim 37, wherein the atleast one water out detection method is disabled when in the firstoperational state.
 45. The method of determining a water out conditionof claim 37, wherein a passive water out detection method is selectedwhen in the second operational state.
 46. The method of determining awater out condition of claim 37, wherein an active water out detectionmethod is selected when in the third operational state or the fourthoperational state.
 47. The method of determining a water out conditionof claim 37, wherein a passive water out detection method in conjunctionwith an active water out detection method is selected when in the thirdoperational state or the fourth operational state.
 48. The method ofdetermining a water out condition of claim 37, wherein a time-basedactive water out detection method is selected when in the fourthoperational state.
 49. The method of determining a water out conditionof claim 37, wherein a passive water out method is run at pre-determinedintervals to constantly check for a water out condition.
 50. (canceled)51. (canceled)
 52. The method of determining a water out condition ofclaim 30, the at least one water out detection method comprising apassive water out detection method, an active water out detectionmethod, and the passive water out detection method in conjunction withthe active water out detection method.
 53. The method of determining awater out condition of claim 52, the passive water out detection methodcomprising: calculating an water level; comparing the water level to athreshold; determining a water out condition when the water level isless than the threshold, and the water level comprising a ratio of anamount of power supplied to the heater divided by a difference between atemperature of the heater minus a temperature of humidified gases. 54.(canceled)
 55. The method of determining a water out condition of claim52, the active water out detection method comprising: controlling atemperature of the heater to a baseline; supplying an amount of power tothe heater until a target is achieved; monitoring heater temperatureuntil a maximum is reached; comparing the maximum heater temperature toa threshold; and determining a positive test result when the maximumheater temperature is greater than the threshold.
 56. The method ofdetermining a water out condition of claim 52, the passive water outdetection method in conjunction with the active water out detectionmethod comprising: determining a water out condition through the passivewater out detection method; and confirming a water out condition throughthe active water out detection method if the passive water out detectionmethod provided a positive outcome. 57-61. (canceled)
 62. The method ofdetermining a water out condition of claim 34, wherein the high flow,unsealed mode comprising set points of 37 degrees, 35 degrees, and 33degrees Celsius.
 63. The method of determining a water out condition ofclaim 34, wherein the invasive mode comprising a set point of 37 degreesCelsius.